Cushioned ceramic driven disc assembly with ceramic friction pads fixed to slotted backer plates

ABSTRACT

A clutch disc assembly for a friction torque device has a clutch damper assembly which includes a hub defining an axis of rotation and a concentric steel disc. The damper assembly includes a plurality of cushion elements fixed to the steel disc. First and second friction rings are disposed on opposite sides of the cushion elements and are rotatively fixed to the steel disc. First and second friction rings have an equal number of inner circumference and outer circumference keyhole slots defining an equal number of mounting areas. A friction pad is fixed to each mounting area, with friction pads on the first friction ring being in substantial alignment with the friction pads on the second friction ring.

RELATED APPLICATIONS

This continuation in part application claims the benefit of U.S.Provisional Patent Application 61/326,354, filed on Apr. 21, 2010 andU.S. patent application Ser. No. 11/895,236, filed Aug. 23, 2007, andU.S. patent application Ser. No. 11/396,445, filed Apr. 3, 2006, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to clutch disc assemblies. Morespecifically, the present invention relates to the mounting of frictionmaterials on clutch disc assemblies and to the arrangement of frictionmaterial on a clutch disc assembly.

BACKGROUND OF THE INVENTION

Motor vehicle clutch driven disc assemblies, or simply clutch discassemblies, employ friction material to define engaging surfaces whichengage facing metal surfaces provided by clutch pressure plates,flywheels and/or intermediate plates. The friction material can beconfigured in a wide variety of arrangements. To cite two exemplaryarrangement, the friction material can be in the shape of a single ring,or a plurality of friction pads. The arrangement selected depends onseveral factors, including but not limited to, the frictionalcharacteristics of the friction material, the available surface area ofthe engaging surfaces, the diameter of the engaging surfaces, theavailable clamping forces, the required torque transmitting capabilityof the clutch, the rotational inertia of the friction material whenapplied to the clutch disc assembly and the wear characteristics of thefriction material. Certain applications are best served by clutch discassemblies employing a plurality of small arcuate sections of ceramicfriction material fixed to a supporting ring shaped backer plate. It hasbeen noted that with this configuration, the pads are subject to tippingduring operation. The tipping results in incomplete clutchdisengagements and an associated difficulty in shifting. It is desiredto provide an arrangement for a clutch disc assembly which allowsceramic friction pads to be employed without generating the undesiredtipping phenomenon.

SUMMARY OF THE INVENTION

The present invention provides an arrangement for a clutch disc assemblywhich allows ceramic friction pads to be employed without generating theundesired tipping phenomenon.

A clutch disc assembly for a friction torque device has a clutch damperassembly which includes a hub defining an axis of rotation and aconcentric steel disc. The damper assembly includes a plurality ofcushion elements fixed to the steel disc. First and second frictionrings are disposed on opposite sides of the cushion elements and arerotatively fixed to the steel disc. First and second friction rings havean equal number of inner circumference and outer circumference keyholeslots defining an equal number of mounting areas. A friction pad isfixed to each mounting area, with friction pads on the first frictionring being in substantial alignment with the friction pads on the secondfriction ring.

Further objects, features and advantages of the present invention willbecome apparent to those skilled in the art from analysis of thefollowing written description, the accompanying drawings and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of and transmission and clutchillustrating the environment of the present invention.

FIG. 2 is a partially exploded view of a clutch disc assembly of thepresent invention.

FIG. 3 is a close-up perspective view of the clutch disc assembly ofFIG. 2.

FIG. 4 is a close-up side view of a second embodiment of the presentinvention.

FIG. 5 is an end view of the clutch disc assembly of FIG. 4 in thedirection of arrow 5.

FIG. 6 is a sectional side view of a friction ring of FIG. 2 in thedirection of arrows 6.

FIG. 7 is a partial angle view of an alternative embodiment a clutchdisc assembly 224 without one of its friction rings.

FIG. 8 is a sectional side view of the clutch disc assembly of FIG. 7with both of its friction ring in the direction of arrows 8.

FIG. 9 is an end view of a clutch disc assembly with friction ringshaving keyhole slots.

FIG. 10 is a is a broken-out side view of the disc assembly of FIG. 9 inthe direction of arrow 10 showing a preferred cookie placement.

FIG. 11 is a perspective view of a friction ring of the clutch discassembly of FIG. 9.

FIG. 12 is an end view of a friction ring of an alternative embodimentof a clutch disc assembly.

FIG. 13 is a broken-out enlarged view of a portion of the friction ringof FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Certain terminology will be used in the following description forconvenience in reference only and will not be limiting. For example, theterms “forward” and “rearward” will refer to directions forward andrearward of a transmission as normally mounted in a vehicle. The terms“rightward” and “leftward” will refer to directions in the drawings inconnection with which the terminology is used. The terms “inwardly” and“outwardly” will refer to directions toward and away from, respectively,the geometric center of the apparatus. The terms “upward” and “downward”will refer to directions as taken in the drawings in connection withwhich the terminology is used. All foregoing terms mentioned aboveinclude the normal derivatives and equivalents thereof.

Referring to FIG. 1 of the drawings, a partial cross-sectional view of aclutch/transmission assembly 10 is shown. An engine flywheel 12 isrotatably coupled to a clutch cover 14. A gear change transmission 16 isnonrotatably mounted to a bellhousing 18 which is mounted to an engineblock (not shown). A clutch assembly 19 including clutch cover 14 andengine flywheel 12 is disposed within bellhousing 18. The transmission16 is driven through the rotation of a transmission input shaft 20 aboutan axis 21 which eventually rotates a transmission drive yoke 22 whichis attached to the balance of the vehicle driveline (not shown).

The transmission input shaft 20 is rotated by the flywheel 12 throughfrictional engagement of a clutch disc assembly 24 with flywheel 12. Theclutch disc assembly 24 is typically nonrotatably slideably mounted tothe input shaft 20 of the gear change transmission 16 and disposedbetween engine flywheel 12 and a clutch pressure plate 26 of assembly19. Commonly shaft 20 and disc assembly 24 have complementary matingsplines enabling disc assembly 24 to axially slide along shaft 20 whilerotating as a unit therewith.

Referring now to FIG. 2, a partially exploded view of clutch discassembly 24 is shown. As shown in FIG. 5, assembly 24 comprises threemain sub assemblies: a clutch damper assembly 28, and first and secondfriction rings 30 and 32 respectively. Damper assembly 28 has aplurality of radially extending cushion elements 34 to which rings 30and 32 are fixed by rivets 35.

First and second friction rings 30 and 32 each include first and secondbacker plates 36 and 38 respectively. Backer plates 36 and 38 are formedof steel. A plurality of first friction pads 40 are fixed to firstbacker plate 36, and a plurality of second friction pads 42 are fixed tosecond backer plate 38.

Clutch damper assembly 28 is typical of such assemblies found inclutches, and is not important in its details. Damping elements 44 inthe form of springs are distributed circumferentially about assembly 28.Damping elements 44 are selected to cushion or damp out drivelinetorsional impulses when disc assembly 24 is clamped between pressureplate 26 and flywheel 12 in a clutch-engaged condition. Assembly 28 isconfigured to permit a limited amount of relative rotation between asplined hub 46 and friction rings 30 and 32. Hub 46 is slideaby disposedon complementary splined input shaft 24 and rotates as a unit therewith.Friction rings are engaged by pressure plate 26 and flywheel 12 androtate as a unit therewith in a clutch-engaged condition. Dampingelements 44 are functionally disposed between hub and friction rings 30,32 in a manner well known in the art to provide the desired isolationbetween the engine flywheel 12 and the transmission input shaft 20.

Cushion elements 34 are well known in the art and can be provide in awide variety of forms. Cushion elements 34 are formed of steel andresiliently axially separate rings 30 and 32. The axially separationprovisions a cushion effect on clutch engagement which aids inmodulating clutch engagement to facilitate smooth clutch engagement.Alternative cushion element configurations equally suited to the purposeare readily found in the prior art. Both backer plates 36, 38 andcushion elements 34 have a plurality of aligned receiving apertures 48and 50 respectively of slightly larger circumference than the body orshank of rivets 35 to enable the body but not the head of rivets to passthere through. Receiving apertures 50 through cushion elements inalignment with rivets 35 connecting first friction ring 30 to cushionelements 34 constitute a first set of receiving apertures in cushionelements. Receiving apertures 50 through cushion elements in alignmentwith rivets 35 connecting second friction ring 32 to cushion elements 34constitute a second set of apertures. First and second engagement areasof cushion elements 34 are axially spaced from each other and aredefined, respectively, by the areas most proximate to apertures 50 inalignment with apertures 48 of first friction ring 30 and with aperture50 in alignment with apertures 48 of second friction ring 32. Aplurality of clearance apertures 52, sized slightly larger than theheads or the formed upsets of rivets 35, are formed in backer plates 36and 38. The clearance apertures 52 in the backer plates 36, 38 are inalignment with the aligned apertures of the opposite backer plate asbest seen in FIG. 2. The clearance aperture 52 receives the rivet upset,or alternatively, the rivet head when the clutch disc assembly 24 isfully compressed in the axial direction.

Clutch friction material is commonly classified as either organic orceramic. Alternative or equivalent characterizations of ceramic frictionmaterial are metallic and cerametalic. In this application, the termceramic will be used generically for any friction materials in theclutch art which may be characterized as any of ceramic, metallic orcerametalic. Organic material is generally characterized as being easierto achieve modulated clutch engagements with. Ceramic material isgenerally characterized as being relatively difficult to achieve smoothclutch engagements with. Part of this difference may be attributable tothe organic material generally being able to deflect more under theclutch engagement loads than the ceramic material. Organic materialcauses less wear of the engagement surfaces of the pressure plate andflywheel. Ceramic material is generally considered more wear resistantthan organic material, and to enable a higher torque transmissioncapacity for a give diametral size and clamp load.

The embodiment of FIGS. 1 through 3 has identical friction rings 30 and32. Friction pads 40 and 42 are accordingly identical and are formed ofceramic material. Direct bonding of friction pads 40 and 42 to annularbacker plates 36 and 38 results in a thinner driven disc and identicalfriction rings than that which is typical for cushioned ceramic materialdriven discs. Thinner disc assemblies 24 are possible because the rivetsdo not pass through the friction pads, and the friction pads 42 do notneed to provide an engagement surface for rivets 35. The precise methodof bonding is not critical to this invention. Two possible methods ofbonding include applying a brazing paste to either the backer plates 36,38 or the friction pads 40, 42 and heating an area of contact betweenthe friction pads 40, 42 and the backer plates 36, 38 causing thebrazing paste to liquefy and bond the friction pads 40, 42 to the backerplates 36, 38. Another method is to form the friction pads 40, 42directly on the backer plates 36, 38 by depositing powdered frictionmaterial on the backer plates 36, 38 and subjecting the powderedfriction material to heat and pressure so that the friction materialsinters or fuses to the backer plates 36, 38 and forms the friction pads40, 42. The powdered friction material is retained by forms duringcompression so it does not spread beyond the desired shape of thefriction pads 40, 42.

Backer plates 36, 38 may be beneficially provided with a coat ofinsulating material 53 to reduce the frictional heat generated duringclutch engagement transferred to the cushion elements 34. Excessiveheating of cushioning elements can result in diminished cushioningcapability. In one embodiment, the insulating material 53 is on a side54 of the backer plate engaging cushion elements 34. The insulatingmaterial 53 needs to provide resistance to the transmission of heat, butneeds not be especially resistant to stress. Insulating material 53 caninclude but is not limited to fiberglass, cork and any phenolicmaterial. Additional insulation may be provided by insulating grommetsdisposed between the rivets and the joint between the facing and thecushion elements 34. The grommets could be in the form of a coating overthe rivet.

A second embodiment of the present invention, as best seen in FIG. 4 andFIG. 5, has organic facing material on a first side of 1 clutch discassembly 124, and ceramic facing material on the second side of thedriven disc. The organic facing material by itself defines a frictionring 130. Friction ring 130 has a plurality of circumferentiallydistributed receiving apertures 148. Friction ring 130 is riveted toengaging cushion elements 34 by rivets 35. Receiving apertures 148 arecountersunk to enable the head or upset of rivets 35 to be disposedbelow an engagement surface 156 of friction ring 130. Alternatively,organic material ring 130 could be bonded to metal backer plate withreceiving apertures passing through the backer plate and rivets 35engaging the backer plate.

In the clutch assembly, driven disc 24 has its organic friction ring 130disposed towards engine flywheel 12 and ceramic friction ring 32disposed toward pressure plate 26. As a result of this orientation, theclutch advantageously provides engagement characteristics similar tothose of a ceramic clutch, while the wear on the flywheel is the same asthat of an organic disc. As a result, the pressure plate sustains morewear than the flywheel over the life of a flywheel disc. This allows aservice technician to replace to replace the cover 14 and pressure plate26 assembly, and to leave the relatively lightly worn flywheel 12 inplace for continued service. This significantly reduces the effortneeded to service a worn clutch.

Yet another embodiment is shown in FIGS. 7 and 8. A perforated steeldisc 258 extends radial from clutch damper assembly. An organic materialfriction ring 230 is fixed to a first side of the steel disc 258 by aplurality of rivets 235. A plurality of cushion elements 234 are fixedto the steel disc 258 on a side opposite the organic material frictionring 230. A ceramic material friction ring 232 comprising a steel backerplate 236 with ceramic friction material 240 disposed thereon is fixedto the cushion elements 234 opposite the steel disc 258 by rivets (notshown). The ceramic friction material 240 can be either in the form ofpads or in the form of an annular ring. Balance weights may beselectively placed in dovetail shaped insert slots 260 within disc 258.

Direct bonding of ceramic friction material 240 to an annular steel ringinstead of direct bonding friction material to smaller backer discretearcuate elements which are in turn mounted separately to the clutchassembly, as done in the prior art, has several benefits. Discreteelements are more prone to hot spots and resultant warpage of thearcuate backer elements. Once source of hot spots will be the variationin displacement due to variation in the cushion elements. In a singlearcuate ring, the variation is minimized because the unitary ringsprevent any single cushion element from creating too much localizeddisplacement. Additionally, having unitary rings results in a strongerstructure for the clutch disc. The invention results in a moreconsistent cushion rate than with arcuate elements.

In another version of the present invention, best shown in FIGS. 9-11, aclutch disc assembly 324 has improved first and second friction rings330 and 332 respectively which are beneficially oriented with respect toeach other. Friction rings 330 and 332 have first and second keyholeslots 360 and 362 respectively separating direct bonded first and secondfriction pads 340 and 342 respectively.

Friction rings 330 and 332 are connected to a clutch damper assembly 328by a steel disc 358, best shown in FIGS. 9 and 10. Disc 358 isincorporated into damper 328 in a manner well known in the art. Theprecise configuration of damper 328 may be consistent with thedescription of damper 28 but is not critical to the present invention.Friction ring 332 is connected to disc 358 indirectly, through aplurality of cushion elements 334 disposed therebetween. Cushionelements 334 are identical to or at least substantially similar tocushion elements 34 and 234. Cushion elements 334 could alternatively beplaced between disc 358 and friction ring 330.

Friction rings 330 and 332 include first and second backer plates 336and 338 respectively. Backer plates 336 and 338 are formed of steel. Asshown in FIGS. 9-11, a plurality of first friction pads 340 aredirect-bonded to first backer plate 336 and a plurality of secondfriction pads 342 are direct-bonded to second backer plate 338. Frictionpads 340 and 342 are preferably formed of ceramic material. Bonding ofthe friction pads is consistent with the above description of bondingpads 40 and 42 to plates 36 and 38. It is appreciated that friction pads340 and 342 could be alternatively fixed to backer plates 330 and 332 byriveting in place of direct bonding. The friction material alone couldbe riveted to backer plates 330 and 332, or first mounted on smallerlocalized backer plates (not shown) which would in turn be fixed byrivets to backer plates 330 and 332. Backer plates 336 and 338 each havea plurality of first and second arms 364 and 366 separated by keyholeslots 360 and 362 respectively. Slots 360 and 362 are open at theirends. Pads 340 are mounted on arms 364 with one edge proximate to andconforming to the shape of adjacent slots 364. In one embodiment, thetrailing edge of friction pads 342 on a cushion-side of backer plate 338is proximate to slot 362. As shown in FIGS. 9 and 10, pad 340 occupiesabout half of the area of first arm 364, extending from an innercircumference to an outer circumference of plate 336 and extendingcircumferentially from one of slots 360 approximately half way to thenext slot 360. Pads 340 and 342 can be either wider or narrower. Asreadily seen in FIGS. 9 and 11, finger slots expand at their base orroot giving the slots 360 and 362 their characteristic keyhole shape.Beneficial effect is illustrated by testing data. Friction pads 340 and342 are provided with clearance apertures to accommodate rivets, but arenot retained or engaged by rivets.

A significant benefit of direct bond and keyhole shaped slots incombination is increased energy absorption with decreased warpage. Totalor near total overlap of friction pads 340 and 342 as best shown in FIG.10 is believed to beneficially contribute to the decreased warpage.Although not easily discerned from the figures, friction pads 340 and342 are also in alignment with cushion elements 334, with the number ofcushion elements 334 equal to the number of friction pads on each offriction rings 330, 332 (consistent with the structure of FIG. 2 whichshows an unslotted friction ring having ten friction pads 42 and 10cushion elements 34). While nine friction pads/slots/arms/cushions areshown, more or fewer may be employed. The outer diameter edge ofassembly 324 has multiple layers best shown in FIG. 10, with the layersfrom side to side consisting of: first friction pads 340 direct bondedto first backer plate 336 which incorporates keyhole slots 360, thebacker plate 336 is riveted to disc 358 which connects to clutch damperassembly 328; a plurality of cushion elements are riveted to disc 358;second backer plate 338 is riveted to cushion elements 334, and secondfriction pads 342 are direct bonded to second backer plate 338. Disc 358may have a plurality of slots 368 equal in number to the slots 360 and362 in backer plates 336 and 338 as shown for disc 258. The radius atthe bottom of the disc slots of disc 258 is not of the keyhole type, butcould be. Test data confirms the effectiveness of this arrangementassembly. A disc assembly having no slots in the backer plates 36 and338 absorbed a total of 1800 BTU before it was significant damaged. Adisc assembly 358 as described above with slots 360 and 362 absorbed atotal of 30,900 BTU without suffering significant damage.

In an alternative structure, not illustrated, disc 358 is of a muchsmaller diameter so that friction rings 330 and 332 do not overlay disc358. Friction rings 330 and 332 attach directly to cushion elements 334which in turn are riveted to an outer circumference of disc 358 similarto the arrangement shown in FIG. 2.

Another embodiment, a clutch disc assembly like those shown in FIGS. 7through 10, differs from clutch disc assemblies 224 and 324 in theconstruction of its friction rings 430 best shown in FIG. 12 and FIG.13. Identical friction rings 430 may be used on both sides of the clutchdisc assembly. The opposing friction rings need not be identical, buthaving identical rings may reduce manufacturer part numbers andcontribute to quality by eliminating any possibility of locating anincorrect friction ring on either side. Friction ring 430 has aplurality of ceramic friction pads 440 bonded to a backer plate 436.

Backer plate 436 has an equal plurality of both outer and innercircumference keyhole slots 460 and 461 respectively separating an equalplurality of mounting areas 464. Each outer circumference keyhole slot460 extends radially inwardly from an open end at an outer circumferenceof backer plate 436 to a closed end having a diameter larger than awidth of a channel portion connecting the open end and the closed end.The channel portion of slot 460 extends radially between the open endand the closed end of slot 460. Each inner circumference keyhole slot461 extends radially outwardly from an open end at an innercircumference of backer plate 436 to a closed end having a diameterlarger than a width of a channel portion connecting the open end and theclosed end of slot 461. The channel portion of slot 461 extends radiallybetween the open end and the closed end of slots 461. Innercircumference keyhole slots 461 extend from an enlarged open endradially inwardly to an open end at an inner circumference of backerplate 436. Slots 460 and 461 are in substantial circumferentialalignment with each other. Each slot 460 and 461 extends less than halfway across the radial distance between the inner and outercircumference. The cumulative lengths of slots 460 and 461 is less thanthe radial distance between the inner circumference and outercircumference of backer plate 436. The gap between the closed ends ofslots 460 and 461 defines a connection portion 465 therebetween. Theradial length of each of slots 460 and 461 is approximately equal.

One friction pad 440 is bonded or fixed by alternative means describedherein, including direct bonding and riveting, to each mounting area464. In the illustrated embodiment, friction pad 464 is retained bydirect bonding. Friction pad 464 has an inner circumference edgeapproximately aligned with an inner circumference of backer plate 436,and an outer circumference edge approximately aligned with an outercircumference of backer plate 436. Friction pad 440 is locatedapproximately midway between the circumferentially limiting edges ofmounting area 440 defined by slots 460 and 461. However, friction pad440 may be place significantly closer to one set of slot edges than theother. The illustrated embodiment shows an arrangement with friction pad440 approximately centered, but clearly closer to one side that theother. Friction pads 440 can vary in shape from that shown in FIG. 12.For example, they could be trapezoidal or rectangular in shape. Pads 440may be relatively wider or narrower than those shown. As with pads 340and 342, pads 440 are provided with clearance apertures to accommodaterivets. As with the embodiment of assembly 324, nine friction pads 440and mounting areas 464 were employed, however, more or fewer may beused. Friction pads of opposing friction rings 430 of a clutch discassembly are substantially aligned, much as shown in the embodiment ofFIG. 10.

In a performance comparison test, clutch assemblies varying only in theconfiguration of the backer plate were subjected to engagements ofincreasing energy. The assembly employing friction rings 430 havinginner and outer slots 461 and 460 clearly evidenced significantly moreresistance to friction-generated heat damage than the embodiment ofassembly 324 employing friction rings 330 having just slots 360extending to the outer circumference.

It should be appreciated that alternatives to the construction of theclutch disc assembly bearing friction rings 430 are available. Forexample, the construction of assembly 124 is one potential alternative.

The foregoing discussion discloses and describes the preferredembodiment of the present invention. However, one skilled in the artwill readily recognize from such discussion and the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the true spirit and fairscope of the invention as defined in the following claims.

We claim:
 1. A clutch disc assembly for a friction torque device,comprising: a clutch damper assembly including a hub defining an axis ofrotation and including a concentric steel disc and including a pluralityof damper springs disposed between the hub and the steel disc; a firstfriction ring rotatively fixed to the steel disc concentric with theaxis of rotation including a first steel backer plate and the that steelbacker plate having an inner circumference and an outer circumferenceand a first plurality of inner keyhole shaped slots radially extendingfrom an open end at the inner circumference to a closed end less and anequal plurality of outer keyhole shaped slots radially extending from anopen end at the outer circumference to a closed end in circumferentialalignment with the inner circumference slots and a gap between theclosed ends defining a connecting portions of the backer plate and theconnecting portions connecting mounting areas of the backer platedisposed between circumferentially adjacent slots and having an equalplurality of friction pads with one friction pad fixed to each mountingarea on a side opposite the steel disc; a second friction ringrotatively fixed to the steel disc concentric with the axis of rotationincluding a second steel backer plate and the second steel backer platehaving an inner circumference and an outer circumference and the firstplurality of inner keyhole shaped slots radially extending from an openend at the inner circumference to a closed end less and an equalplurality of outer keyhole shaped slots radially extending from an openend at the outer circumference to a closed end in circumferentialalignment with the inner circumference slots and a gap between theclosed ends defining a connecting portions of the backer plate and theconnecting portions connecting mounting areas of the backer platedisposed between circumferentially adjacent slots and having an equalplurality of friction pads with one friction pad fixed to each mountingarea on a side opposite the steel disc; and a plurality equal in numberto the first plurality of cushion elements fixed to the steel disc andaxially disposed between the friction rings.
 2. A clutch disc assemblyas claimed in claim 1 wherein the steel disc extends radially betweenthe first and second friction rings and is axially disposed between thecushion elements and one of the backer plates, and has a plurality ofslots equal in number to the first plurality.
 3. A clutch disc assemblyas claimed in claim 1 wherein the steel disc has a smaller outerdiameter than an inner diameter of the first and second backer plates,and the backer plates are connected directly to the cushion elements.